The present invention relates to energy recovery devices and in particular to devices installed in the exhaust of heating equipment to recover waste heat.
It is known to install a fluid conducting coil in the chimney of a furnace to capture waste heat flowing therein. However, many of these devices restrict the updraft of the chimney. For some chimneys or flues it is not feasible to withdraw a significant amount of waste heat from the exhaust without dangerously reducing updraft. Since the updraft depends upon the operating conditions of the furnace as well as wind conditions, the coil inserted in the flue or chimney ought to be conservatively small to avoid a back pressure that might cause exhaust to leak into the furnace room.
The difficulty of sustaining sufficient updraft is acute for embodiments employing a known double helical heating coil in a chimney. While the double coil is relatively efficient its increased surface area tends to restrict updraft.
Known heat recovery systems have provided alternate exhaust paths, a heat recovery coil being installed in one of these alternate paths. In the latter instance the alternate paths are manually controlled by an operator whenever he wishes to recover exhaust heat. The systems employing alternate exhaust paths do not efficiently extract waste heat since their heat recovery coils are relatively inefficient and must be designed very conservatively to avoid interfering with updraft as conditions change dynamically.
Accordingly, there is a need for an effective heat recovery device which can withdraw a significant amount of waste heat from the exhaust of heat producing equipment. Furthermore, such heat recovery devices ought not to interfere with the normal updraft.